1. Field of the Invention
The present invention relates to an automatic focusing system and, more particularly, to an automatic focusing system capable of moving to a desired position an automatic focusing (AF) area in the image pickup area of a camera on which automatic focusing is performed.
2. Related Art
A contrast method is ordinarily used as an automatic focusing (AF) method in image pickup systems such as television cameras in which an image of a subject is converted into an electrical signal (image signal) by an image pickup device (CCD or the like). In the contrast method, a contrast in a subject image taken in by an image pickup device is detected from an image signal (video signal) for the subject image, and focusing of a picture-taking lens (focusing lens) is controlled so that the contrast is maximized, thus automatically performing focusing to the best focus.
In ordinary cases, AF based on the contrast method is performed not on the entire subject in the image pickup area of a camera, i.e., the area of a subject or a subject image through which an image imaged through an optical system is effectively taken as a picture, but on a subject within a restricted portion of the image pickup area. For example, an image signal for a predetermined area on which AF is to be performed in an image signal for a subject image effectively taken as a picture by an image pickup device is extracted and focusing is controlled on the basis of the extracted signal for the predetermined area so that the contract of the image is maximized. In this way, AF is restrictedly performed on a subject within a restricted area. In the present invention, the area on which AF is performed is referred to as “AF area” and a frame indicating the bounds of the AF area (the contour of the AF area) is referred to as “AF frame”.
In ordinary cases of fixing one AF area at a predetermined position in the image pickup area, the AF area is a rectangular area set at a center of the image pickup area. However, cameras are known in which an AF area can be changed to a desired position by a designation operation performed by an operator (see, for example, Japanese Patent Application Laid Open No. 2002-365519. As a method of designating the position of an AF area, a method has been used in which a direction designation member (AF area movement designation member) such as a joystick or a track ball in a predetermined AF area designation section is operated to move an AF area in a suitable direction with respect to the image pickup area and to thereby move the AF area to a target position.